Vehicles may have a fuel vapor recovery system which includes a fuel vapor storage canister (e.g., carbon canister) for trapping fuel vapors from the fuel tank that may contain vaporized hydrocarbons, for example. During engine operation, the trapped fuel vapors may be purged from the fuel vapor canister and released to the engine intake for combustion. In some examples, the pressure in the fuel vapor recovery system needs to be greater than the intake air pressure in order for the purge flow containing fuel vapors to enter the intake. Beyond the pressure difference, a flow of air that is not saturated with fuel vapor is often required to strip the adsorbed hydrocarbons from the canister's HC storage sites. When an engine is boosted, for example, the intake air pressure, such as in the intake manifold, increases above atmospheric pressure and thus there may be insufficient pressure differences available to draw the purge flow into the engine intake.
The inventor herein has recognized the above problem and has devised an approach to at least partially address it. Thus, a method for an engine in a vehicle is disclosed. The method comprises, under a first operating mode, cooling an alternator coupled to the engine via an airflow generating device, and, under a second operating mode, purging a fuel vapor canister by assisting flow into the fuel vapor canister via the airflow generating device.
In this manner, the airflow generating device may be used to increase the flow rate or pressure of the purge flow through fuel vapor canister during conditions when the airflow generating device is not needed to cool the alternator, yet increased purge flow is needed, such as when the alternator temperature is less than a threshold temperature, for example, and when the manifold air pressure is relatively high. As such, the purge flow may be more easily routed to the intake manifold during conditions such as when the engine is boosted. At the same time, when alternator cooling is needed, the device can provide such cooling. Thus, the approach can achieve improved performance by obtaining double duty from a single airflow generating device.
Alternately, one may choose to provide that same alternator air flow rate through an ejector and thus provide suction with which to draw fuel vapors from the canister and pass them into the engine inlet air stream at an appropriate point. In this way, the canister functions conventionally thus avoiding design changes necessitated by having to change the system to a “vapor push” system from a “vapor pull” system.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.